With increasing industrial development, diverse electronic devices are used to achieve various purposes. An electronic device comprises a plurality of electronic components. Generally, different kinds of electronic components are operated by using different voltages.
As known, a power supply is essential for many electronic devices such as personal computers, industrial computers, servers, communication products or network products. Usually, the user may simply plug a power supply into an AC wall outlet commonly found in most homes or offices so as to receive an AC voltage. The power supply will convert the AC voltage into a regulated DC output voltage for powering the electronic device. The regulated DC output voltage is transmitted to the electronic device through a power cable.
Generally, power supply apparatuses are classified into two types, i.e. a linear power supply and a switching power supply (SPS). A linear power supply principally comprises a transformer, a diode rectifier and a capacitor filter. The linear power supply is advantageous due to its simplified circuitry and low fabricating cost. Since the linear power supply has bulky volume, the linear power supply is not applicable to a slim-type electronic device. In addition, the converting efficiency of the linear power supply is too low to comply with the power-saving requirements. In comparison with the linear power supply, the switching power supply has reduced volume but increased converting efficiency. That is, the switching power supply is applicable to the slim-type electronic device and could comply with the power-saving requirements.
Although the switching power supply has higher converting efficiency, there are still some drawbacks. For example, even if the electrical energy is not required to be transmitted to the system circuit of the electronic device, the switching power supply is continuously operated to issue an output voltage having the rated voltage value. In other words, the switching power supply continuously consumes electrical energy even if no electrical energy is transmitted to the system circuit of the electronic device. Under this circumstance, the conventional switching power supply fails to meet the power-saving requirement.
Therefore, there is a need of providing an improved power conversion circuit so as to obviate the drawbacks encountered from the prior art.